Experimental Inquiry on Draught in Ploughing. 241 



plough, and to 20 that are pulling a bad one. I must add^ that 

 Lord Moreton's ploughman thought our own horses would work 

 as well as his own if they were as well fed. I doubt myself 

 whether they are so formed as to w^alk with ease at the same 

 pace. There is one circumstance, however, which tends to re- 

 move what certainly may appear extravagant in this calculation, 

 although the calculation rests upon facts which can easily be 

 disproved if they are incorrect. It arises out of another experi- 

 ment which I made, and as the results are, I believe, new, and as I 

 think they are curious, I will venture to trouble the Society with 

 a short statement of that experiment in conclusion. 



In the beginning of these trials I had imagined that if one 

 plough were drawn more rapidly than another, its apparent 

 draught would be unfairly increased in consequence of its having 

 moved a greater quantity of earth during the time of its trial ; and 

 precautions were taken accordingly : it soon appeared, however, 

 that a slight addition of speed did not raise the numbers marked 

 by the draught- gauge. At last, therefore, I determined to ascer- 

 tain, if possible, what was the actual effect produced by increased 

 speed on the draught of the plough. This was first tried Avith 

 Clark's plough on the moory ground, described already in the ac- 

 count of the fourth day's trial. The Scotch horses were made to 

 go along the 5 and the 6-inch furrows at the slowest pace to which 

 they could be restrained, not so slow a one^ however, as I have 

 lately seen in other horses at the same work. The draught was 

 24 stone in the 5-inch furrow, and 22 in the 6-inch one, which I 

 suppose was on lighter land. They were next urged to the utmost 

 speed of their walk-, more than double their former rate ; but 

 though more than a double quantity of land was of course ploughed 

 in the same time, the draught was only raised from 24 to 25 or 

 26 stone in the one furrow, and from 22 to 23 in the other. 

 The extreme slightness of this increase would have surprised 

 me still more, had I not learnt in the course of these trials how 

 large a portion of the draught of the plough is occasioned by 

 its friction against the soil, how small a part by the splitting, 

 raising, and throwing over a certain weight of earth. Thus, in 

 the trial at Lyford, a bystander pointed out to me that while 

 one of the ploughs was being accidentally drawn down a furrow 

 already opened, such was the adhesion of the clay^ that the gauge 

 actually marked as high a draught at that time as turned out 

 afterwards to be the average of the plough's work in the same 

 field. Now, friction is, I believe, often not increased by increased 

 rapidity of motion in the two bodies rubbing against each other. 

 But, in the draught of the plough, we have its own weight pressing 

 against the bottom of the furrow, and that pressure increased by 

 the weight of the furrow-slice, the latter weight not increasing. 



